Higher alpha olefins having 6 or more carbon atoms are important as comonomers in polyolefins and as intermediates for detergent compounds. For example, 1-hexene and 1-octene are used as comonomers in LLDPE (linear low density polyethylene) and 1-decene is used as a starting material for the production of synthetic lubricants. However, there have hitherto only been general methods, and not targeted syntheses, for preparing most of these higher alpha olefins. These general methods tend to produce mixtures of the desired higher alpha olefins with other olefinic products, e.g. internal olefins. For example, the dehydrogenation of higher paraffins leads to a mixture of olefins which mostly contain internal double bonds. As another example, olefins having a relatively high number of carbon atoms and terminal double bonds can be prepared by the oligomerization of ethylene using transition metal catalysts, for example, by the Ziegler process, the SHOP process of Shell or the Ethyl Process. However, the mixtures obtained have to be separated sometimes by very complicated methods if a particular alpha olefin is to be isolated. In addition, ethylene is a very expensive feedstock material which results in a higher price for alpha olefins obtained by oligomerization.
For these reasons it would be desirable to provide a process for producing alpha olefins in a targeted manner from starting materials other than ethylene.
U.S. Pat. No. 5,124,465 and U.S. Pat. No. 5,191,145 disclose a process for preparing linear higher alpha olefins by successive transalkylation reactions. In these publications, a linear, internal olefin having from 4 to 30 carbon atoms or a mixture of such olefins is reacted with trialkylaluminium in the presence of an isomerization catalyst. This results in the formation of a trialkylaluminium compound in which at least one of the alkyl radicals is derived from the olefin used. This radical is present as a linear alkyl radical derived from the alpha olefins which has been formed by isomerization. The trialkylaluminium compound is subsequently reacted with an alpha-olefin in a displacement reaction in which the linear alpha-olefin which was bound to the aluminium is liberated. This process allows internal olefins to be isomerised effectively and in good yields to produce terminal olefins. However, the process is a pure isomerization reaction which does not make it possible to increase the chain length. The internal olefins used for the isomerization come from the usual sources and a targeted synthesis of alpha olefins having a desired chain length is not possible by means of the process.
U.S. 2004/0199035 and U.S. 2004/0054241 (BASF) relate to processes for preparing higher alpha olefins by a combination of isomerising transalkylation reactions with metathesis reactions. However, in order to make 1-octene from transalkylation/metathesis methods, it is necessary to start from 1-pentene. It would be desirable to produce 1-octene from 1-butene since 1-butene (present in Raffinate-II which is described below) is a relatively cheap and abundant feedstock compared to 1-pentene.
It would be desirable to provide methods for producing higher alpha olefins in a selective manner and, which, particularly for cost reasons, makes use of feedstocks other than ethylene, particularly relatively cheap feedstocks such as Raffinate (II) which contains a mixture of 1-butene and 2-butene.